Motors are widely used to drive semiconductor packaging equipment, such as wire-bonders in wire-bonding machines. Linear motors are generally preferred to drive wire-bonders as they offer fast and precise motion. During such driving motion, a large amount of heat may be generated, whether due to a large current flowing through the motor or a significantly large resistance in the coil wires because of the compact size of the motor. Cooling is critical not only to prolong the useful life of the motor but also to maintain its performance.
Electrical fans are commonly used to cool most equipment in the industry. However, although electrical fans are useful for external cooling, they are insufficient to cool internal components of linear motors, which generate and retain the most heat. In the case of linear motors comprising a coil disposed between a pair of magnets, there are small gaps between the coil and magnets. These gaps are not easily accessible to cooling air generated from an electrical fan. A practice has thus developed of trying to guide cooling air into the said gaps.
One way of guiding cooling air into the said gaps is to drill holes and nozzles inside a moving coil bracket of a linear motor, and to channel cooling air through these holes and nozzles. The problem is that if the material of the coil bracket is not metallic or its machining property is poor, drilling long holes and nozzles inside the coil bracket is expensive and sometimes may not be possible. It would also increase the moving mass of the motor if additional material is formed in the coil bracket to house such holes and nozzles. Another way is to drill air nozzles on a stator of the motor. This also has limitations because such nozzles generally direct compressed air along only one axis. If in use, the moving coil moves along another axis, some portion of the cooling air will not reach the coil surface when the coil bracket moves away from the nozzle, and cooling air is wasted.
Yet another method of implementing a cooling system in a linear motor is found in U.S. Pat. No. 5,834,862 for a “Linear Motor Cooling System”. This patent discloses a nozzle mounted on one end of a moving coil bracket for producing two high velocity sheets of air which are directed horizontally over the surfaces of the coil so as to bring down the temperature of the coil. This cooling structure is located outside the magnets of the linear motor and is not efficient especially if the coil area is large. Moreover, this patent disclosure introduces cooling air from one end of a coil bracket without proper sealing, allowing some of the cooling air to escape into the atmosphere. Furthermore, the nozzle area is relatively large, which serves to reduce the air pressure of the cooling air and reduces its ability to reach more remote areas of the coil. It may also not be effective if the whole coil bracket is designed to move in both the X- and Y-axes.